The present invention relates to a technique for recording/reproducing stream data in a magnetic disk drive. More particularly, the invention relates to a control method for easing the performance requirement of specific seek operations and to a magnetic disk drive using this control method.
Today, it has become part of our daily life to record/reproduce image data, particularly moving images, to/from a magnetic disk drive.
In the past, image data was usually recorded/reproduced as an analog signal to/from a magnetic tape medium by using a video recorder.
Recently, it has become relatively easy to record/reproduce images by personal computers through digital signal processing. CD, DVD, MO, optical disk drives, optomagnetic disk drives and others are being used as media and devices to record/reproduce images. Devices named HDD recorders have become popular, too.
Magnetic disk drives are convenient when used for temporary storage before image data is moved to removable media. Its features may be summarized as below:
1) Usually, the personal video recorder (hereafter abbreviated as PVR where appropriate) employs MPEG2 as the recording format.
Image data according to MEPG2 is composed of I frames obtained by compression within each frame and B and P frames which describe differences between frames.
In the PVR, when a single stream of image data is reproduced or recorded, the magnetic disk drive is accessed four to five times per second.
2) When another stream is read for fast forward replay while a stream is reproduced or recorded, it is necessary to quickly read I frames for fast forward replay while data is recorded to a continuous area four to five times per second.
3) When two stream data are recorded or reproduced semi-concurrently, accessing is substantially random.
Even when the two streams have the worst positional relation, sufficient performance is required. Meanwhile, when one stream is read for fast replay while another stream is recorded or reproduced for normal replay, the two streams requires different data transfer rates.
4) The control circuit bears a large load to semi-concurrently record/reproduce streams. Therefore, it is possible to cause a problem if an ordinary seek operation is inserted during the semi-concurrent operation.
When two stream data are recorded/reproduced, relatively long-range seek operations are done between an inner area and an outer area on the magnetic disk medium.
Since the rate of data read and transferred to the host machine is not changed depending on the seek range, it has been thought that longer-range seek operations impose harder performance requirement on the magnetic disk drive.
In this situation, the inventors have found that although long-range seek operations are done when two stream data are accessed semi-concurrently, the seek time may be set longer contrary to general belief since one of the two streams can use a high data transfer rate area (outer area on the magnetic disk).
In conventional seek profiles, the seek speed is made faster as the number of tracks to be passed or the travel distance increases although long-range seek operations necessary for concurrent recording/reproduction can be set slower than ordinary seek operations. This is not adequate in terms of noise level and power consumption.
In addition, since the magnetic disk drive, as an external storage device of a computer, is required to provide high access performance, high rigidity actuator components are used so as to move the magnetic head to a target track as fast as possible with suppressed vibrations. This makes cost reduction difficult.
There are techniques to execute a seek command in such a manner that the head is moved to the target sector of the target track not as fast as possible but as timely as possible by taking latency into consideration (just in time seek). For example, disclosed in Japanese Patent Laid-open No. 1989-245471 is this kind of technique for making seeking operations slower without the lowering the seek performance. However, this technique does not take into consideration accessing image data.
Disclosed in U.S. Pat. No. 5,901,009 is a technique for shaping the actuator control signal so as to remove sharp changes and reduce seek noise (reduced noise seek) when a seek command is executed. In that technique, the seek time is always made longer regardless of the seek length.